Electric circuits for reducing the effect of shunt capacity or reactance introduced by circuit elements



PEICI l@ Q BLUMLEIN 2,149,331

ELECTRIC CIRCUITS FOR REDU'CING THE EFFECT OF SHUNT CAPACITY OR REACTANGE INTRODUCED BY CIRCUIT ELEMENTS Filed July 8, 1936 3 'SheenS-Sheet l /NVENTOR A. D- B UMLE/'N I ATTORNEY 2 .Tv e e h Y QW T C A e www CNS TwMLS NE UL HE S T F .l OUA C l MRS NEG% IF, EFYl LEB M@ WTWVM u GD BWMJ Dcm .1 AMEV. C RN OA FT C SA TUM IR CR RO 1 March 7, 'N392 ELEC TRIS //VENTOR A. D. BLUMLE/N 'ATTO/mm UNITED STATES PATENT OFFICE ELECTRIC CIRCUITS FOR REDUCING THE EFFECT OF SHUNT CAPACITY OR RE- 1iiICTAN CE IN'IRODUCEDy BY CIRCUIT ELE- ENTS Alan Dower Blumlein, Ealing, England, assignor to Electric & Musical Industries Limited, a British company Application July 8, 1936,

In Great 7 Claims.

Serial No. 89,676 Britain July 8, 1935 The reduction which can conveniently be eiTected by the known of electric resistances and the inherent capacity of inductance coils. The invention relates more particularly, but not exclusively to l rangements which are l like signals; thus if a D. C. coupling is effected load if the valve is one which is required to be ween two valves by connecting a battery bedissipate considerable power, the load resistance tween the anode of one valve and the control must be of a robust construction so as to be giid of the other, the stray capacity of the batcapable of passing substantial current without teiy to eai th or chassis may result in a relative ovei heating, and its self-capacity may be so high attenuation of the higher frequencies of the sigthat relative attenuation of the higher frequennals to be amplied Similarly, when a thermicies of the signals to be amplified takes place omc 'valve has a load impedance arranged in its A similar eiect may be present when the anode cathode circuit the stray capacity of the cathodecircuit load is constituted by a choke coil, the heating battery, or other souice, to the chassis stray capacity of the coil serving as a relatively 5 may introduce a similar relative attenuation of ow impedance shunt at the higher frequencies the higher frequencies. Furthermore, the stray The inherent inductance of a load resistance in capacities may produce other harmful effects, a theimionic valve amplifier may give rise to such as undesired phase shifts. undesirable resonances with the stray shunt ca- It has already been proposed, in order to avoid pacity, or, if the latter has been substantially the eiects of the capacity to earth of a coupling eliminated by a method such as that of this inbattery, to connect the poles of the battery to Vention, may produce a relative accentuation of the higher frequencies. reactances may produce mote from the battery being connected together such as undesired phase shifts.

g3 through a condenser. Such an arrangement is,

however, of restricted application,

amount of reduction of effective stray capacity such, for example, as resistances and inductance ,m which they provide; thus, foi example, it may coils With the previously proposed arrangehappen in a D. C. amplifier that grid current ment, since the resistances are often requii ed to flows during operation at peak signal amplitudes, be of high value and to pass substantial current and if the resistances are too large, there may be serious amplitude distortion.

of only a few inegohms.

order of inegohrns or quired to deliver power.

One feature of the invention consists in a circuit arrangement which includes an element (or elements) which introduces undesired stray capacity or reactance and in which for the purpose of substantially eliminating the effect of the stray capacity or reactance, building-out means are provided which, together with said element (or elements) cause the circuit, as a result of a combination of inductance and resistance, to simulate substantially a pure constant resistance.

Another feature of the invention consists in a circuit arrangement comprising a circuit element which, in operation, is required to carry relatively large currents, wherein, for the purpose of reducing the effects of the inherent shunt capacity of said element, there are provided in series with said element with respect to a source of power, building-out means comprising a resistance and an inductance coil in shunt withl one another, said resistance being one rated to carry less current than that carried, in operation, by said element, and wherein said building-out means are so constituted and arranged that, together with said circuit element, they simulate substantially a pure resistance.

The invention further provides a circuit arrangement comprising a circuit element which is required to have negligible inductance and which, in operation is required to carry relatively large currents, wherein for the purpose of reducing the effects of the inherent inductance effectively in series with said element, there are provided in shunt with said element with respect to a source of power, building-out means comprising a resistance and a condenser in series with one another, said resistance being one rated to carry less current than that carried, in operation, in said element, and wherein said building-out means are so constituted and arranged that, together with said circuit element, they simulate substantially a pure resistance shunted by the self-capacity of said element.

The circuit element may be a resistance, in which case the resistance selected to form part of the building-out means is one having a relatively small power-dissipation rating; the powerdissipation rating of a resistance decreases as its power to carry current without overheating decreases. In this way, the inherent capacity and inductance of the building-out resistance can be made negligibly small compared to that of the resistance constituting the circuit element.

A further feature consists in a circuit arrangement comprising a circuit element which has stray capacity to earth, said element being connected between two points in said circuit between which, in operation, a potential difference is required to be established, wherein between each of said points and said element respectively there is provided a resistance of a magnitude such that the eiects of said stray capacity are to some extent reduced, and wherein a path which permits the passage of alternating current is provided between the ends of said resistances remote from sai-d circuit element, characterized in that, for the purpose of substantially eliminating effects of said stray capacity, the circuit is provided with building-out means vsuch that the circuit simulates substantially a pure constant resistance. A still further feature of the invention consists in a circuit arrangement comprising a circuit element which is associated in series with a rst conductor and has stray capacity to a second conductor, wherein, in order to reduce or eliminate the effect of said stray capacity, an inductance-coil is provided between each of the terminals of said circuit element and the points of connection of said element to ,said first conductor,

'ing paragraph may,

the two coils being coupled to one another by" mutual inductance and wherein there are pro-n vided damping means for substantially reducing or eliminating the effects of resonances within a predetermined working range due to said coils and the said stray capacity.

The first conductor referred to in the precedfor example, be the lead between` the anode of a thermionic valve and the control grid of a further valve, or it may be the filament of a valve. The second conductor may, for example, be the chassis of an ampliner, or any other part of the circuit arrangement the potential of which does not vary substantially in operation; the second conductor may be connected to earth. K

The circuit element referred to mentioned feature may be one which is required, in operation, to deliver power; in this case, the arrangement according to the invention provides the advantage that the inductance coils which are vemployed to hold off the stray capacity o thev circuit element may be arranged to cause only a' relatively small drop of potential.

The damping means may comprise a arranged in shunt with the stray capacity, or two resistances arranged in shunt with one or both of the coils and with the stray capacity respectively; where two resistances are employed, the arrangement may be made such that these resistances form with the coils and the stray capacity a composite circuit which simulates substantially a pure resistance. This composite circuit may forni the whole or a part of the load impedancel of a thermionic valve.

A coupling condenser may be connected between the ends of the coils remote from the circuit element the coupling condenser tending to by-pass the coils and the circuit element for currents at frequencies in the upper part of the working range. Means may-be provided for reducing or eliminating the effects of resonances between the coils and the coupling condenser.

For the purposes of this specification, the term earth is to be accorded the meaning usually attributed to it in the radio and allied arts; thus the expression having stray capacity to earth covers not only cases in which the circuit element has stray capacity to physical earth, but also cases in which the circuit arrangement is isolated from earth and is built up on a chassis or like structure to which the circuit element has considerable capacity.

Various embodiments of the invention will be described, by way of example, with reference to the accompanying drawings in which:-

Fig. 1 illustrates a typical circuit to which the invention may be applied.

Figs. 2 and 3 illustrate the application of the invention to the substantial elimination of the eiects of the stray capacity of a battery serving to bias the anode of a cathode ray tube of the transmitting type as shown in Fig. l.

Figs. 4 and 5 show diagrammatically D. C. amplifiers according to the invention.

Fig. 6 illustrates the application of the invention to reducing the effectsof the self-capacity of the anode load resistance of a thermionic valve.

Fig. 7 shows a modification of the arrangement of Fig. 6 in which the anode load comprises a choke coil.

Fig. 8 illustrates a further embodiment of the invention, as applied to the reduction of the selfcapacity of a resistance.

resistance one of the coils or with in the last Y vmitted are set up in a load f Fig. 9 illustrates the application`of' the'lnvention to the reduction of the inherent series 1nductance of a resistance.

Fig. 10 shows a part of a D. C. coupled amplifier according to the invention.

Fig. 11 illustrates the application of the invention to a modulator which is required to work over a wide range or" frequency down to zero frequency.

Fig. 12 shows a circuit arrangement according to the invention in which means are provided for reducing the effects of stray capacity due to a source of cathode heating current.

Fig. 13 shows a modication of the arrangement of Fig. 12 in which provision is made for the supply of bias potential to the control electrode of a subsequent valve, and Fig. le shows a modification of the arrangement of Fig. 13.

of the object to be transmitted is cast upon the photo-electric mosaic surface thus formed and The elements on the right of the signal plate are scanned by an electron beam from an electron gun (not shown). The elements used to return to a and currents representative of the light and shade of the imag-e to be transresistance 4 which is connected between the signal plate 2 and earth. Potential differences are thus set up between the be fed by means of lead 6 to the input of an ampliiier.

It is desired to apply a difference of potential between electrode I and the signal plate 2; if

. were directly connected between elec- The battery 'I is accordingly connected between electrode I and point 5 through two series re sistances IS ci value, a by-pass condenser I I of a capacity which is large compared with the capacity 8 being connected between point 5 and electrode I. The e'ective shunt impedance across load resistance fi is then the resultant of capacity 8 in series with the two resistances 9, IU in parallel. By making resistanfces 9, E!! of sulciently high value, for example one or two megohins each itis semetirees possible to arrange that this effective shunt impedance has a negn ligible effect on the frequency characteristic of the tube 3 and its associated circuits over the range of frequencies to be handled.

In some cases, however, the shunt impedance may still cause an undesirable amount of attenuation of the highest frequencies, and it may be inconvenient to compensate for this by increas- 3 I for the following reason; the photo-electric current between signal plate 2 and electrode I is through the circuit Si, l, ifi, and the higher resistances 9 and it are made, the larger is the voltage drop ing resistances 9 and the return path for as 9 and I il, is limited.

According to the invention, therefore, the residual shunt impedance is built whole circuit, including the shunt impedance, f

behaves as a required inductance for coil verse of C and (r-R) about the resistance R. In Fig. 2, the inductance coil I2 has a magnitude L, and is shunted by a resistance I 3 of magnitude r', load resistance Il having the magnitude R as before; r is made equal to In this example, the

I3 of Fig. 2 may be recircuit such as that 2`1 Fig. 4 shows a circuit but used to provide a two valves I4, of a direct-coupled ainplier. In Fig. 4, the battery (which may, if desired, be replaced by any other suitable source of potential, such as a rectifier), serves to maintain the potential of the grid I of valve I5 at a suitable value with respect to the anode l1 of valve Iil, and resistances S, I3 are provided to hold olf the stray capacity, represented by condenser 8, of the battery to earth; the anode resistance 4 an inductance similar to that of Fig. 2,

departing from the spiritV resistance I3 in parallel, these ele- 5 in the part of the Y direct coupling between circuit is required to have above the predetermined frequency referred to. The effects of the substantially constant The resistance 6 and have self-capacities which are small of the series resistance of coil Coil 'I may be air-cored, or may have a core of comminuted magnetic material.

In Fig. 8 the valve Winding l2 to the core, and thus to chassis, is held off (or prevented from having an undesirable eiect) in the manner described by means of the coupled choke coils earth or Where C is the magnitude of stray-capacity I3, and R is the value of each of resistances I6 and I8, and the arrangement I8 as l2 to ductance, shown dotted at 20, of magnitude L1, as well as self-capacity shown dotted at 5. To

series with a Resistances 4 and 2| are given the same magnitude, R, and it is arranged that C1 is such that the relationship The self-capacity of resistance 4, which is indicated by 5, can be built out as shown in the manner described with reference to Fig. 6.

pled to one another by mutual inductance; the resistance 34 represents the resistance of battery 27 and the inherent resistances of chokes 28 and According to the present invention, therefore, damping means are associated with the chokes, or with the stray capacities or with both in order to damp out such resonances. In Fig. 10, resistance 32 serves eiectively as a damping resistance across capacity 3|, and the resistance 30 arranged a frequency at 6 in shunt with choke 28 may also serve a damping function. By a suitable choice of the values of the damping resistances, it can be arranged that the impedance of the coupling circuit as a whole, within adesired working range of frequency, does not vary by more than about 120% 'due to resonances between the chokes and the stray circuit capacities.

In a preferred arrangement, however, the coupling circuit is made to simulate a pure resistance, or a purely resistive network; thus, if the capacity 3l is equal to C, and the resistances 30 and 32 are both of the same magnitude R, then the parallel aiding inductance L of chokes 28, 29 is made such that the relationship L=CR2 is substantially satisfied; in these circumstances, assuming the two chokes to be coupled as tightly as possible, so that the series impedance introduced thereby is n-egligible, the whole coupling circuit simulates a pure resistance of magnitude R, this pure resistance constituting the anode load of valve 23. If desired, this valve may have a separate load resistance 33, shown dotted, and resistance 32 may then if desired be taken to earth instead of to the positive terminal of the anode current source. By taking resistance 32 to the positive terminal of the source, however, loss of current is avoided.

The coupling between chokes 28 and 29 need not be so tight as that effected by winding the chokes in a bilar manner, or on a common magnetic core; in the case in which the coupling is looser than this, it is preferably arranged that the mutual inductance between the chokes 28, 29 is substantially equal to the inductance of coil 28, that is, the coil which is shunted by a damping resistance.

If the chokes 2B, 29 are air-cored and are required to be of large inductance, the length of wire in each choke 28, 2S may be such that at some frequency within the working range, a resonance occurs between the coil and its distributed self-capacity, the resonance usually occurring at which the length of wire in the coil is substantially half a wavelength. The effect of this resonance is that, at the resonant frequency, the impedance of the chokes becomes very low; the effect can be avoided by making either or both the coils 28, 29 in a plurality of separate sections, each section having in shunt with it a separate damping resistance; thus each coil may be wound in two halves, each half being damped by a resistance equal to Now it may be found that the series opposing inductance of the chokes 28, 29 resonates within the operating frequency range with condenser 3S, and this residual may be damped by means of series resistance 35; preferably, however, resistance 35 is given the same value, say T, as resistance 35i (which, as has been explained, may be made up to a suitable value) and it is arranged that C where l is the series opposing inductance of chokes 28, 29 and c is the capacity of condenser 33; the series impedance between the anode of valve 23 and the grid 25 of valve 24 is then a pure resistance equal to 1'.

vTft will be noted that, in the amplifier described, the grid 25 of valve 24 may be allowed to become positive relative to the cathode thereof-in other words, grid current may flow, without the introduction of substantial wave form distortion, since the grid circuit of valve 23 is one of relatively low resistance; it will of course be observed that when grid current flows, battery 21 serves not only as a source of bias, but also to supply power.

Fig. 11 shows a circuit of the same general character as that shown in Fig. l0, and illustrates the application of the invention to a direct coupled modulator suitable for a wide range of frequencies.I In Figs. 10 and 1l the magnitudes of components; bearing like references are denoted by like symbols; referring to Fig. ll, the valve 23 is arranged t0 establish modulation signals across the modulation resistance 33, the floating anode battery high-tension rectifier or other D. C. source 21 being inserted between the anode 31 of valve 23 and modulation resistance 33 and serving as a D. C. coupling. The end of the modulation resistance 33 remote from earth is connected to the input of a radio frequency modulator (not shown). The source 21 of anode potential is connected into the circuit through two mutuallycoupled inductances 23, 29, which are arranged to present as small an impedance as possible for the passage of normal anode electron current, which flows from the valve 23 through inductance 28, through the source 21, through inductance 29 and so to the modulation resistance 33.

The two inductances are preferably tightly coupled, for example, by being wound on a common magnetic core.

ance 38, and similarly the capacity 3 l., which rep.

resents the capacity of source 21, to earth to.- gether with any capacity which.v it; may be convenient to add thereto, is shunted by a resistance 32, resistances 39, 3.2 having, as before, the same magnitude R. The combined battery feed and coupling circuit then appears as a resistance of value R between the anode of valve 23 and earth, provided the parallel-aiding inductance of the two chokes equals CR2.

If desired, the resistance 33 may be omitted, the composite resistance R then constituting the whole modulation resistance. If resistance 33 is included in the circuit, the effective modulation resistance is R in parallel with the resistance 33. If the source 21 is a rectier, the latter may conveniently be built out to simulate a pure resistance equal to r less the series resistance of the two chokes, and built out again as described with reference to the drawings, to correct for the leakage inductance of the tightly-coupled chokes. Furthermore, resistance 38 may be divided into two parts, each equal say to 2R, one shunted across each of chokes 28, 29.V Again it will be noted that the D. C. component of the anode current of valve 23 is dissipated in resistance 32, and Vthis resistance can have substantial self-capacity, since such self-capacity forms part of the capacity 3 I.

Fig. 12 illustrates the application of the'invention to circuits for feeding current to the cathode of a valve which is operated, for example, with its load in the cathode circuit. Such a valve may be one known as a cathode follower, the potential of the cathode of which can be arranged sublf the coupling is less tight than l, this, it is preferably arranged that the mutual'i inductance is substantially equal to the inductto the earth core 39, oi to both the primary windlated from the other two windings on account of ing and the core. In this case, filament 38 conthe higher voltage of rectifier 44 The insulation situtes the first conductor The eects of the of the composite choke, from end to end must stray capacity, which is indicated in dotted lines be such as to be capable of withstanding the peak by condenser 3|, which will be referred as C, is amplitude of the output of valve 31. The inducteliminated by feeding the lament 38 through ances of coils 28, 29 are preferably made sub- 10 two tightly-coupled chokes 28, 29. 'I'hese chokes stantially equal, and the average mutual inductare shunted by a resistance and a further reance between the coil 45, and the coils 28, 29 is sistance 32 shunts the stray capacity 3|. The preferably made substantially equal to the averend of resistance 30 remote from earth is taken age inductance of coils 28, 29.

to the centre tap 4| on a low resistance 42 across The cathode rectifier 43 and the cathode are the filament 38, and the two halves of resistance shuntecl by resistances 46, 42 respectively, the i'n parallel constitute in eiect a portion of centre points 41, 4| of which are connected resistance 30. through resistance 39. The resistances 46, 42 are esired th ances 28, 29 requires to have a low self-capacity garded for purposes of design as forming part 2Q and has tc carry heavy currents, so that thick of resistance 3U. 'I'he stray capacity 3| of rec- L' wire is necessary, it is advantageous to wind the tier 43 and the stray capacity 3| of rectifier 44 inductances 28, 29 on a magnetic core resembling are eliminated in the manner discussed with refa transformer core, but having a large gap (preference to Fig. 12.

erably in the middle of the coil) and formed of The centre point 4| of the resistance 42 Very thin laminations. As the filament current the upper end of the choke winding 45 are conpasses through the coils in series Opposition, the nected by a resistance 48 and a condenser 49 in core is not magnetized by the filament heating series; the magnitudes of components e8 and e9 of the valve 31. The transformer capacity 3| tier 44 as seen through the leakage inductance 30 also comprises the self-Capacity of the resistof the composite choke, is effectively a pure reance sistance. Any capacity due to the windings of AS in the Drei/1011s arrangements 0f Figs. l0 the choke which effectively shunts the leakage inductance of chokes 28, Z9 is equal to CR?, R by amodiiication of the circuit employed to build 35 The capacity to earth of a battery, machine, 01 by application of the principles already discussed rectifier feeding the lament with direct current which govern such building out, In this way, the

may be effectively eliminated in a similar manner. effective Stray Capacity across the Cathode iead CaSe it iS required 110i? Only to supply Cathode and due solely to the choke coils. If the choke heating current to the valve 31, but also tc Supply is suitabiy designed and particularly if i1; is given 's, in general, 45 the grid of which requires, instead of the poslpossible te eieei; e, reduction ef Str tive potential of the cathode 38 of the valve 31, es much es 10:1 for a frequency ra a negative potential relative to earth. The valve from 0 te 2 me 31 works into a load resistance arranged in its Diiieuities maybe encountered i tion into effect 50 resonances within bias to the valve 50, which it is assumed is liable refereneee to run into grid Current 0n eXtreme amplitudes Referring to Fig. 14, a doubly-wound choke 65 The CathOdc-Crcuit lOd 0f ValVc 37 is formed by comprising coils 5| 52 is connected in the leads two resistances Sil, 32 in series, of which resistto the grid bias reetier 44, Coil 52 being conance 32 is required to dissipate the heat produced neeted in series with eeii 45 and by thc 'steady and 10W frequency space Currentcennected between the rectiner and Resistance 30 is only required t0 dissipate the 41 on resistance 46. Resistance 32 is, as in Fig. 70 heat produced by the high frequency alternating 13, connected between the left hand terminal of by means of a triple-wound choke coil, the three across coil 5|. windings 28, 29 and 45 of which are coupled to- It will be seen that coils 5|, 52 do not have to gether as tightly as possible. The two windings carry the heating current for valve 31. Coil 5| and 25 carries only the 'anode current of valve 31 and coil 52 carried only the grid current oi the valve 5e. It is therefore readily possible to make the inductance of the doubly-wound choke Ei, 32 substantially greater than that of the triply-wound choke 28, 29, d5. Ii C2 is the value of the capacity 3i' to earth of rectiiier Mi, L2 the magnitude of the inductance 5l and R1 the magnitude of resistance 32 and also of resistance 53, then this part of the circuit behaves as a pure resistance if L2=R12C2- The capacity C2 may be regarded as comprising in addition to capacity 3l', the shunt stray capacity of resistance 32.

If C1 is the magnitude of the capacity 3l, to earth, of rectier 43, if L1 is the effective inductance of the triply-wound choke as seen from the cathode 33, and if resistance 3Q has a value R1, then the whole system behaves as a pure resistance if L1=R12C1, and if L2 has the value given above.

In the circuit of Fig. 13 the necessary inductance L1 of the triply-wound choke 28, 29, d5 is given by L1=R12(C1-\-C2), C1 and C2 having the values given above. many cases C1 is much less than C2 and therefore, by employing the circuit oi Fig. 14 instead of that of Fig. 13 the magnitude of the inductance of the triply-wound choke can be very much reduced.

It will be seen that in the arrangement of Fig. 14 the stray shunt capacity 3i of rectifier 43 is shunted by resistances 53 and 32 in series with one another, resistance 32 being also in shunt with the stray capacity 3l of rectifier M.

In practice, it may be preferable to provide heating current for the cathode by means of a direct current generator instead of from a rectifier. If this method is employed, the generator is `connected in place of rectifier i3 and, by well yspacing and insulating the generator from earth, it is possible to keep capacity 3i small compared with the capacity 3i of the oating rectier M.

It is to be noted that, provided it is relatively small, the self-capacity of coil 5i may be included in the effective value C2 of capacity 3i.

The source 43 of cathode heating current may be so shielded that it has capacity to rectifier Q4. only. In this case the upper end of coil 5| is connected to tapping point ii instead Iof to tapping point li'l, and the upper end of coil 52 is connected directly to the right hand terminal of condenser dg, coil i5 being omitted. It will then be seen that the stray capacity of source 43 is shunted by resistance 53 and the circuit so constituted is in series with the eiective inductance of coils 28, 29 shunted by resistance 3B. This part of the circuit is arranged to form a substantially constant resistance network by application of the principles already stated. The stray capacity of rectifier lli is shunted by resistance 32 and is built out by inductance 5i shunted by the resistance network last referred to, to form a further substantially constant resistance network.

The above description is given by way of example only and many modifications of the invention, within the scope of the appended claims, will be apparent to those versed in the art.

What is claimed is1- l. A coupling circuit between two thermionic elements comprising a condenser connected to a current carrying electrode of one of said thermionic elements, a load resistance connected to a current carrying electrode of one of said thermionic elements, a circuit element connected in said current carrying" electrode circuit and having dis'' tributed capacity to ground, said distributed capacity being small as compared with said condenser, a pair of resistances for connecting the circuit element in parallel with said condenser, a resistance, an inductance connected in parallel to said resistance and inserted in the connection between said load resistance and the coupling circuit whereby the entire coupling circuit will be in eiect a substantially constant resistance over substantially the frequency range transmitted by the thermionic elements, said eifect being accomplished by making the ratio of the inductance to said distributed capacity equal to the square of the load resistance 2. A coupling circuit between two thermionic elements comprising a condenser, a circuit element having distributed capacity to ground, said distributed capacity being small as compared with the condenser, a pair of resistances for connecting the circuit element to the coupling circuit in parallel with said condenser, and a load connected to said coupling circuit comprising a resistance with an inductance and resistance connected in parallel therewith whereby the entire coupling circuit is effectively a constant resistance over substantially the entire frequency range to be transmitted by said thermionic elements, the value of the ratio of said inductance to said distributed capacity being such as to equal the square of the resistive value of the load on said thermionic elements L 2 c R) 3. A coupling circuit between two thermionic elements comprising a condenser, a source of current having distributed capacity to ground, said distributed capacity being small as compared with the condenser, a pair of resistances for connecting the source of current to the coupling circuit in parallel with said condenser, and a load connected to said coupling circuit comprising a resistance with an inductance and resistance connected in parallel therewith, whereby the entire coupling circuit is effectively a constant resistance over substantially the entire frequency range to beV transmitted by said thermionic elements, the value of the ratio of said inductance to said distributed capacity being such as to equal the square of the resistive value of the load on said thermionic elements L 2 c R) 4. A circuit arrangement comprising an electrical resistance which, in operation, is required to carry relatively large currents, means for reducing the effects of the inherent shunt capacity of said resistance comprising a second resistance and an inductance in shunt with one another, said second resistance being one rated to carry less current than that carried, in operation, by

said rst resistance, and means for connecting said second resistance and inductance in series with said iirst resistance whereby, together with said first resistance, they simulate substantially a pure resistance, the ratio of said inductance to said capacity being such as to substantially equal the square of the value of both of said resistances current capacity connected in series with said rst inductance, and two resistances of substantially to said first reactance whereby the ratio of into capacitive reactance in the the square of the load resistive value the wnole of the band of frequencies transmitted by said electronic devices.

7. A coupling circuit for two thermionc devices comprising a circuit element connected in a current carrying electrode circuit of one of said thermionic devices, said element having a determindistrbuted capacity,

trode and substantially tributed capacity, a resistance connected serially with said circuit element, an inductance connected in shunt with said resistance, the ratio of the value of said inductance to the capacities being equal to the square of the resistive load in said current carrying electrode whereby the coupling circuit formed by said elements simulates a substantially constant resistance over the entire range of frequencies transmitted by said thermionic elements, and means said coupling elemen ALAN DOWER BLUMLEIN. 

